When harvesting windrowed crops with a pick-up attachment mounted on the header of a combine harvester or when cutting the crops close to the ground surface with a direct-cut attachment, stones and other hard foreign objects inadvertently may be picked up and fed to the threshing mechanism, which thereby is exposed to severe damage. To prevent these foreign objects from entering the threshing mechanism, combine harvesters commonly are equipped with a trough-shaped stone trap disposed between the threshing mechanism and the normal crop elevator which conveys crop material from the crop gathering attachment to this threshing mechanism. Foreign objects which are fed towards the threshing mechanism are hit by threshing bars thereof and, as a result, are projected into the stone trap.
The crop elevator commonly is in the form of a feeder housing enclosing a chain-and-slat apron conveyor which entrains crop material and feeds the same rearwardly through a discharge opening of the feeder housing proximate to the threshing mechanism. The stone trap thus is positioned with its inlet opening generally at the transition between said discharge opening and the threshing mechanism with the stone trap itself being positioned below the plane of that transition. In other words, as seen from the front of the combine, the stone trap is positioned below the rearward end of the feeder housing.
Details of a combine harvester equipped with a conventional stone trap can be taken from EP-A-0.096.923, the content of which is included herein by reference.
A common problem which is occasionally experienced with conventional stone traps is the failure of foreign objects, such as stones, to automatically drop out of the stone trap upon the opening of the discharge door thereof. The reason therefore may be the machine vibrations which cause the loose material in the stone trap to become densely compacted and stick together thereby preventing this material, inclusive the foreign objects therein, to fall out of the stone trap by gravity when the stone trap door is opened. Operation in wet crop conditions may have the same effect to the extent that, in these conditions, dirt and crop particles in the stone trap may form a muddy, sticky mass which equally fails to fall from the stone trap under influence of gravity when the stone trap door is moved to its dumping or discharge position.
The stone trap door conventionally may be opened from the side of the combine harvester by means of any appropriate control means often including overcenter latching means. If the content of the stone trap fails to fall to the ground under gravity upon the opening of the stone trap door, the operator has to crawl underneath the crop elevator and to remove the stubborn content of the stone trap manually. However, as the stone trap, by its nature, is filled not only with foreign objects such as stones, but also with chaff, short pieces of straw and lots of dust, especially when harvesting crops in dry conditions, it readily will be appreciated that there is operator reluctance to remove the foreign objects manually from this awkward position underneath the feeder housing, knowing that, by doing this, a dusty and unhealthy atmosphere is created around the operator.
The need for crawling underneath the feeder housing for manually correcting a failed automatic emptying of this stone trap, has been obviated by the present invention.